There are various types of IC packages in which semiconductor elements are packaged. For example, one type is called a land grid array (LGA) in which plate-shaped pads are disposed on an undersurface thereof and a type called a ball grid array (BGA) in which spherical pads are disposed on an undersurface thereof. When electrically connecting the IC packages of various types to wiring on circuit boards, IC sockets including contacts electrically connected to the wiring on the circuit boards are conventionally used (See Japanese Patent Laid-Open No. 2005-19284, for example).
FIGS. 14(A)-(B) are views schematically showing a part of a conventional IC socket 90 which receives an IC package 80 of a type called LGA. The IC socket 90 includes an insulating housing 91, and the insulating housing 91 is provided with a recess 915 which receives the IC package 80 from above. A plurality of contacts 95 are disposed in the recess 915 of the insulating housing 91. The contact 95 has a cantilever spring with a free end at a side of a contact point 958. The IC package 80 has a circular electric contact pad 81. Part (A) of FIG. 14 shows the state in which the IC package 80 is set in the recess 915, and part (B) of FIG. 14 shows the state in which a normal load is applied to the IC package 80 in a direction shown by the arrow by a cover (not shown).
As shown in part (A) of FIG. 14, when the IC package 80 is set in the recess 915, the contact points 958 of the contacts 95 arranged in the IC socket 90 contact electric contact pads 81 disposed on an undersurface of the IC package 80.
FIGS. 15(A)-(C) are views showing the contact 95 included in the IC socket 90 shown in FIG. 14. Part (A) of FIG. 15 shows a front view of the contact 95, part (B) shows a left side view, and part (C) shows a plan view.
The contact 95 has a base 954 which engages with the insulating housing 91 and is long in a vertical direction, and a spring member 953 which is folded back on the base 954 from a side edge of the base 954. The spring member 953 has a folded portion 955 which is folded from the side edge of the base 954, and a contact arm 956 which extends upward from the folded portion 955. The contact 95 includes a connection member 957 extending downward from the base 954. The shape of the spring member 953 is formed by the contact arm 956 extending diagonally from the folded portion 955 on the same plane as the folded portion 955 being folded at the border with the folded portion 955. Specifically, as shown in part (C) of FIG. 15, the contact arm 956 extends at an angle δ with respect to a perpendicular line of a surface of the base 954 in plane view. Thereby, when the contacts 95 are disposed in the insulating housing 91 with high density, the contact arm 956 can be kept long while avoiding the contact arm 956 contacting other adjacent contacts 95.
In the IC socket 90 which adopts the contact 95 shown in FIG. 15, when the normal load is applied to the IC package 80 in the direction shown by the arrow shown in part (B) of FIG. 14, the contact arm 956 of the contact 95 bends downward and the IC package 80 sinks down. At this time, the contact point 958 slides in a horizontal direction on a surface of the electric contact pads 81, whereby oxide films on the electric contact pad 81 and the contact 95 are scraped off, and connection is kept favorable. In the example of part (B) of FIG. 14, the contact point 958 slides in the right direction in FIG. 14.
Incidentally, when the contact point 958 slides on the electric contact pad 81, the IC package 80 receives the force which moves in the horizontal direction, as shown in part (B) of FIG. 14. When the IC package 80 receives the force in the horizontal direction, there arise the problems that the IC package 80 is prevented from sinking down, and the portion of the insulating housing 91, on which the IC package 80 is pressed, is scraped. Thus, in order to reduce the force which moves the IC package 80 in the horizontal direction by sliding movement of the contact points 958, it is conceivable to dispose a group of the contacts 95 in an orientation opposite from another group of the contacts 95, and to cancel the forces received from the contact points 958 of the respective contacts 95. However, in this case, angular momentum occurs in the direction to rotate the IC package 80 in plane view as will be described below.
FIG. 16 is a plane view showing the state in which the contact 95 included in the IC socket 90 shown in FIG. 15 bends. A solid line shows a state in which the normal load is applied, and the contact 95 bends, and a broken line shows a state in which the normal load is not applied to the contact 95. The angular momentum applied to the IC package 80 is obtained by adding up the products of the distances from a center of the IC package 80 to the contact points 958 of the respective contacts 95 and forces fi acting on the contact points 958 with respect to all the contacts 95 disposed in the IC package 80. However, in plane view, the direction in which the contact arm 956 extends has the angle δ (see part (C) of FIG. 15) with respect to the perpendicular line of the surface of the base 954, and therefore, the direction of the force fi which determines the angular momentum deviates from the direction in which the contact arm 956 extends. Specifically, the force fi includes a force fy in a direction in which the contact arm 956 extends from the folded portion 955 in plane view and a force fx in a direction perpendicular to the force fy. Here, the extent to which the direction of the force fi deviates depends on the amount by which the contact point 958 moves on the contact 95 as the contact 95 bends, and friction of the contact point 958 of each of the contacts 95 with the electric contact pad 81. Therefore, it is difficult to cancel the forces fi acting on the contact point 958 when seeing them with respect to the entire IC socket 90 and the IC package 80.